This invention is directed to a method for measuring the thickness of a refractory in metallurgical apparatus, and more particularly to measuring the thickness of a refractory laid-up against the interior surface of the steel sheel of a metallurgical apparatus, for example a blast furnace, electric arc furnace, basic oxygen furnace, etc. The device used to measure the thickness of the refractory is also described.
Apparatus, for example, metallurgical furnaces and mobile hot metal transport, for example blast furnaces, basic oxygen furnaces, electric arc furnaces, open hearth furnaces, submarine ladles, stationary hot metal mixers, glass refining furnaces, power house boilers and the like, are constructed of a steel superstructure or steel shell and a refractory supported by the superstructure or laid-up against the interior surface of a steel shell. The refractory confines the heat and hostile atmosphere within the apparatus and protects the surrounding environment and/or steel superstructure and steel shell of the apparatus.
In recent years, much effort has been expanded to develop improved refractory. These efforts have resulted in an increase in the life of the refractory and have increased the length of furnace campaigns, i.e., the time a furnace is in service before a reline of refractory is required. Such efforts are continuing since the longer the time a furnace is in operation the fewer relines are required and the lower is the cost of producing molten metals in the furnace. Many of these efforts have been directed to monitoring the wear or erosion of the refractory so that timely repairs can be made to the refractory to prolong the campaign of the furnace and to prevent catastrophic failures of the refractory.
Several devices and methods for monitoring the wear of the refractory in metallurgical furnaces are disclosed in U.S. Pat. No. 3,078,707 to L. G. Weaver entitled "Thickness Gage for Blast Furnace Wall", U.S. Pat. No. 3,307,401 to G. S. Bachman entitled "Element for Measurement of Furnace Wall Thickness and Temperature", U.S. Pat. No. 3,532,797 of H. K. Lunig entitled "Apparatus for Monitoring Thickness of Wall Lining of Electric Arc Furnace" and U.S. Pat. No. 3,512,413 to O. VonKrusenstierna et al. entitled "Measuring Body Capable of Being Built into the Wall of a High Temperature Furnace". All the monitoring devices disclosed in the above patents are essentially thermocouples having two dissimilar metals. The devices operate on the principle of electrical resistance masurements and rely on the discontinuity of an electric circuit. Bachman and Weaver use "ladder-like" devices extending through the thickness of the refractory while Lunig and Krusenstierna et al. rely on a plurality of paired resistance wires of various lengths positioned at various depths in the refractory thickness. In actuality the monitoring devices do not continuously monitor the thickness of the refractory in the sense that a direct thickness measurement is made continuously. The thickness of the refractory is actually known, or determined, only at the time of a disruption in the electric circuit and is only approximately known when the circuit is again completed.
The prior art devices enumerated above are limited to measuring fixed thicknesses that are dependent upon the position of a particular wire or loop in the refractory. These types of devices are also susceptible to being "shorted-out" by slag penetration, breakage due to spalling of the refractory, and deterioration of the sheath and insulating material placed between the wires and the sheath. Then, too, the number of refractory surface positions or thicknesses of refractory which can be measured by these devices is finite. For each new position, a separate wire or loop must be added to the monitor body.
Another method for measuring the thickness and monitoring the wear of the refractory is the use of sources of low level radiation, i.e. radioactive isotopes. A plurality of the sources are embedded at predetermined locations in the refractory during reline. When a source ceases to emit radiation, erosion at that location is indicated. Since the actual erosion is known only when radiation ceases, it can be seen that this device and method are similar to the other devices and methods in that the thickness and erosion of the refractory is not known until the source disappears. Radiation type monitoring is thus not really a continuous measurement system. Handling of the radioisotopes must furthermore be done by specially trained and licensed personnel. If any isotopes remain in the refractory after a furnace campaign, special care must be taken by the licensed personnel to recover the isotopes.
There is therefore a need for an inexpensive, safe, substantially continuous method for measuring the thickness of a refractory in a metallurgical apparatus particularly while the apparatus is in service.
It is an object of this invention to provide a method for measuring the thickness of the refractory in a metallurgical apparatus, for example a blast furnace, basic oxygen furnace or electric furnace, etc. wherein at least one monitoring device is positioned in a critical wear area of the refractory laid-up against the interior surface of the steel shell of the apparatus and the device is connected to an electronic instrument which induces timed pulses in the device and records and displays reflected signals of the impulses, which display is indicative of the length of the device and thickness of the refractory.
It is also an object of this invention to provide a simple monitoring device suitable for use with an electronic instrument which uses the time-domain reflectometry techniques, whereby the thickness of the refractory can be measured either continuously or intermittently.